[Qemu-devel] [PATCH] Handle SDL grabs failing

[Qemu-devel] [PATCH] Handle SDL grabs failing

[Mark McLoughlin]

If a X window is not viewable, XGrabPointer() fails and
returns GrabNotViewable. SDL's X backend currently handles
this by retrying the grab until the window becomes viewable
again.

This means e.g. if you Ctrl-Alt-RightArrow to switch
workspaces, QEMU tries to grab, SDL blocks because the
window isn't viewable and your guest stops executing until
you switch back to that workspace again.

See this Fedora bug for the gory details:

  https://bugzilla.redhat.com/480065

Some SDL backends will return SDL_GRAB_OFF from
SDL_WM_GrabInput(), so the fix is to make the X backend do
this if the grab fails.

The only side-effect in QEMU is that if SDL_WM_GrabInput()
fails we still change the window title to indicate that it's
grabbed, when in fact it's not. This patch fixes that minor
issue.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
---
 sdl.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/sdl.c b/sdl.c
index 15427c5..2ce6e81 100644
--- a/sdl.c
+++ b/sdl.c
@@ -286,9 +286,12 @@ static void sdl_grab_start(void)
         SDL_WarpMouse(guest_x, guest_y);
     } else
         sdl_hide_cursor();
-    SDL_WM_GrabInput(SDL_GRAB_ON);
-    gui_grab = 1;
-    sdl_update_caption();
+
+    if (SDL_WM_GrabInput(SDL_GRAB_ON) == SDL_GRAB_ON) {
+        gui_grab = 1;
+        sdl_update_caption();
+    } else
+        sdl_show_cursor();
 }
 
 static void sdl_grab_end(void)
-- 
1.6.0.6

Re: [Qemu-devel] [PATCH] Handle SDL grabs failing

[Anthony Liguori]

Mark McLoughlin wrote:
> If a X window is not viewable, XGrabPointer() fails and
> returns GrabNotViewable. SDL's X backend currently handles
> this by retrying the grab until the window becomes viewable
> again.
>
> This means e.g. if you Ctrl-Alt-RightArrow to switch
> workspaces, QEMU tries to grab, SDL blocks because the
> window isn't viewable and your guest stops executing until
> you switch back to that workspace again.
>
> See this Fedora bug for the gory details:
>
>   https://bugzilla.redhat.com/480065
>
> Some SDL backends will return SDL_GRAB_OFF from
> SDL_WM_GrabInput(), so the fix is to make the X backend do
> this if the grab fails.
>
> The only side-effect in QEMU is that if SDL_WM_GrabInput()
> fails we still change the window title to indicate that it's
> grabbed, when in fact it's not. This patch fixes that minor
> issue.
>
> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
>   
Nice catch!  This has been a long standing bug.

Applied.  Thanks.

Regards,

Anthony Liguori